The present invention relates to a nozzle for spraying liquid.
A nozzle for spraying liquid is generally a component comprising a hollow inside, called a swirl chamber, connected on one side to a feed source, and whose wall opposite the inlet is generally of hemispherical shape. An outlet orifice opens out into the generally hemispherical shaped end wall of the swirl chamber, which outlet orifice has, at the point where it opens out into the swirl chamber, a much smaller cross-section, not more than half, and preferably less than one fifth, of the transverse section of the swirl chamber. In general, the outlet orifice widens towards the outside moving away from the swirl chamber, but this is not obligatory.
By virtue of this particular shape, the liquid passing through the nozzle, subjected to an abrupt succession of compression and depression, bursts out into multiple droplets. The outlet orifice may have a circular cross-section or a flattened cross-section, depending on the shape of the jet of droplets which it is desired to obtain.
Spray nozzles which have the object of giving greater speed to a jet of liquid, without, however, causing it to burst out into droplets, have a distinctly different shape, with progressive narrowing, possibly followed by a widening which is also progressive. The progressiveness of the variations in cross-section leads to an increase in the velocity of the jet without the dispersion of the latter.
The size of the droplets formed at the outlet of a spray nozzle of given dimensions and shape depends, inter alia, on the pressure of the liquid in the swirl chamber.
With conventional spray nozzles, for a given nozzle and liquid, there is a correlation between the flowrate of the liquid and the pressure of the latter, and therefore the size of the droplets. In numerous technological fields, it would be desirable to be able to vary these parameters independently of one another. For example, it may be desirable to vary the flowrate whilst keeping the size of the droplets constant. This is the case, for example, in agricultural technology, where the size of the droplets determines the effectiveness of treatments with phyto-sanitary products, but in which the quantity of products laid down by unit surface area must remain constant, which implies that the flowrate of the nozzle must be adjusted to the speed of displacement of the carrying vehicle. It is also the case in many other technological fields, for example the moistening of paper or cloth as a function of their water content inside a processing machine. In other cases, it may be desirable to vary the size of the droplets, for example in order to modify their cooling effect, without being obliged simultaneously to modify the flowrate.
It would be desirable to be able to have use of a nozzle which allows action on the size of the droplets and the flowrate of liquid, independently of one another.
Of course, such a nozzle must be inexpensive, robust and easy to maintain.
Proposals have been made, see for example UK Patent No 951,589, German Patent No 17430, U.S. Pat. No. 3,776,470, for devices allowing the shape, and consequently the performance of nozzles for spraying jets of liquid to be modified, but nothing has been written or suggested for applying similar techniques to spray nozzles. The reason for this is doubtless that it is more difficult to deform a component containing a swirl chamber with a hemispherical wall, followed by a narrow passage orifice, than a conventional jet spray nozzle. Indeed, a conventional jet spraying nozzle may be made from a component with a thin wall, which is easy to deform. In contrast, a spray nozzle necessarily consists of a solid component, in which the spray chamber and the outlet orifice are hollowed, and it doubtless seemed impossible at the time to deform such a component in a controlled fashion.
In German Patent Application No 2,439,226, a spray nozzle was proposed whose end is composed of a block of elastic material, inside which the swirl chamber and outlet orifice are hollowed. The object of this arrangement is not to modify the shape of the nozzle at will, but to allow, by deformation of the orifice, the escape of a foreign solid which would come to block the nozzle, the latter then resuming its habitual shape.